1. Field of the Invention
The invention in general relates to antenna structures, and more particularly to flexible omnidirectional dipole antenna arrangement.
2. Description of the Prior Art
The use of lighter-than-air vehicles as high altitude platforms for communication equipments has been known for many years. By suspending electronic payloads from a stabilized platform beneath an aerodynamically shaped balloon, called an aerostat, point-to-point and omni-directional communications can simultaneously be accommodated. The aerostat is generally tethered at an altitude of several thousand meters to provide ground area coverage of several hundred thousand square kilometers.
For each system the payload configuration depends upon the particular application and a typical payload might include commercial and educational TV, AM and FM radio broadcast equipment, off-the-air receivers, translating equipment, high and low density wide band communications equipment for fixed and mobile multichannel voice and data transmission, to name a few. The electronic systems utilize a variety of different antennas some of which may be mounted on the stabilized platform suspended from the aerostat, with the antennas, as well as the electronic equipment, being protected from the environment by an aerodynamically shaped windscreen.
For some applications such as mobile telephone communications, a relatively long rigid antenna is required for a base station and this presents a mounting problem. For such mobile telephone use where the aerostat is in effect the base station, the antenna must radiate and receive omnidirectionally, however, if the relatively long antenna is merely suspended beneath the wind screen to achieve omnidirectionality, it structurally interferes with the tether and is subject to wind loads.
The aerostat has an air-filled tail assembly the interior of which may serves as a protective mounting location for the rigid antenna. However, for many operations it would be desired to fill the tail assembly with helium to give added lift to the structure and the inclusion of the elongated rigid antenna in a helium atmosphere would be undesirable.
Another possible mounting location for the antenna would be on the outside surface of the areostat hull. However, there is an incompatibility due to the fact that a relatively long rigid member has to be firmly secured to a relatively soft flexing member and in addition to a mounting problem, there is the danger of tearing the fabric of the aerostat hull.